Method and apparatus for separating audio frequencies



194a W. SOLLER A A 2,455,389i

METHOD AND APPARATUS FOR SEPARATING AUDIO FREQUEINCIES Filed Feb. 14, 5 Sheets-Sheet l M A4 I v y l v [fiii L .1. 00 '3' 2 W 7 1% J4- V '49 INVENTOR.

I ATTORNEY Dec. 7, 1948. w, SOLLER 4 2,455,389

METHOD AND unmrus FOR smmnume wnro summons 7 Fi led Feb. 14, 1944 s Sheets-Sheet a 2 22-71. I Saa S ANPlIF/[ll j 65 I l ANIPZLFIQA-VPI IN VEN TOR.

Patented Dec. 7, 1948 UNITED .ISJ'I'ES .EIN T QfiFiFl-GE "METHOD-AND APPARATUS FOR SEPARAT- ING AUDIO FREQUENCIES 1Walter..Soller, Cincinnati, Ohio, .assignor of one- .halItiftoTWilliam'H. WoddinpJxa, 'San"Ma.teo, iCa

' :wADpliemtion-February 14, 1944, Serial No. 522,344

11 Claims. (Cll178-44) 11 1.2 My invention -relates-broadlyto frequency selectaken on line I-l, ofnEiggzwand ,withcertainibf :tion,=andwmore'zparticulai ly toia-systemrofewave the-parts shown in top plan view; Eig.f2"is a analysis ebasednon.ithe pmoduction-iof-spectral by transverse sectional iview taken on lin 2-'. -2 ,of

diffraction throughiwave interference. Fig. 1;.Fig. 3 is a 'viewt'aken on 111163- 73 of, Rig. 1

One of the objects .ofi .mys-invention-is to pro- 5 illustrating Dartsof the-apparatus in 'sidejfelevavidea unethodand apparatus iolsseparatingand .tionan'd showing thetasingifl.transversescction; selecting audio frequenpyvibrations from a com- ..'Fig. 4.is.a fragmentary view on an. enlarged; scale .-plex .mu1ti:- frequency audio Irequencyvibration. of one of the connecting means, established with -Anther ob3ect :013 my immnizionis to provide a the. physical body 'foriu'tilizing .a lpa'rticulariirecompact construction of;irequencywselector ap- 1o.querlcywithinithe.comP "f que 1py raggelof paratus upon-whioh -z'complex: audio frequencies the physical body, the view being. taken onf'line may be impx essedaand selected audio .I-requencies 4-1 of 'FigI5fFig; is a transversesedtionatview "within the range :of ptheuimpressed frequencies takenon line 5- 5.v of Fi 4 fili'igifi is a schematic -se1e0-ted;f0r' transmission tQseparatechanneIs. circuit'diagram illustratinathe mannenof. estab- .Still,-an0the1= object ofi mydnventionistopro-1 lishin'g connectionsktoseparate alldi-DTIQQHEHQY vide an-zar rangementiofaaudio frequency selector channels from' thelfrequency selectorappamtus apparatus z-in twhichaa multiplicity of .com'plex of my invention LFjg'." 7 is aschematic view iil audio.IrequencIeSsmayobQ impressed upon the .tra'ting the connectionobfgthe output. circuits of input-s1de;-0f\ the -equipmentaandsselected audio the frequency selector apparatus through, a millfrequenci-estwithintherangeiofstheimpressed Het ple tube circuit, of the tap lc veredmy myFP quenciesdelivered-satetheroutput sidesofathe ap e t".. ,010,'dated August 6, 0;"fofM IIQ P paratus. vacuum tube, .for transmittingselected ,alitlid'fre- Another opject, ofwmyoinvention. is,- to .provide quen'cies to different "line circuits F s- 8.12mi 9 san arrangementoiimassiveibodytinto whichcomare theoretical diagrams "expla n "l t En plex'vibrationsiwithimthe audio vattwumelicy range Verse "Wave ry i h"mYiDYBntiOn is may, be -lniwoducedi,anda seleotediaudiofrequencies based? Fi 10 a t r theoretit ltldi ram -derived through mechanical oonnections.withthe w n the-meth df -p opa 't ni o t e m =l-massiveabody foraselecting, z -throngh :transverse 'verse waves through the"physicar-bdd emnlpyed Mme vibrationswpwnticular.frequencies-withinqthe "in the .system'of my invehibionilllig fil r fi q-anger-ofi -the audjo f gqugncigs 030 one 11181311611 0? establishing 8;- connection *bBtWGIGn n-As-still funther-sopjeet.sofsmyinwention:..is, l the ma-in-vibratory-source of complex' f'requenbies i rpltovide ea ocompact aJ-OQIIStFHGflOIi of irequency FhY I' y Showingmovementtdrived l selectiomappanmtus -for; operation (Within the audio Y a--r p c dwibraitiolf e "diretion F P ragge 1. mu a a h ica .b q i 12 shows diagrammatiealiy tmsmovemene'a-pro- -mounted etc :-recei-ve:.mmn1exevibrations which .135 fluc ara-repr dueedwibration rin the oppasite establish transverse waves through the physical di-TBCtiOm 'FigLB iliustrates-oneqnthdd ---bo.dy-.-which mayr-be utflmedu-iforwrthenselflctiDn of e a e e t fr quency from the -r h'ys k *mdy :individuahaudiodeequeneies within the. complex by change in resistancezin rthe input-imam of an "fmquengy 1ange amplification. channelydilig. l4iiHustrateszsaimanifitilhanothemohjecti:ofi-my zinwenitionfis tq/pro- +40 nervof changing. eapaiuity-i.aomss-ithezinpntmimuit videiaz'consmmtiemoi apparatuslin which-vibraofs l m 1mcaition'c channel .zunder controlmfi a .tions are :esta'lilished otnztarimaterial bQfi y sand .l selected frequencystderivedzfmmmhernhysicahbmiy rtransversemawesrutflizedun the. bodnkfoeexomng 1 d 5: 1u m a mn arrangement Ion canindividualezeaudioizfu'equenw-zrmponsive members trolling the :inductance Df'Jtheiinpuliicilcflitkbflfin ;iomthe-rseleritiombmfrequenciesewithin the rangeiiamplifieation vnhannel 13in amee with a oithedmpressgdfimmmeg .tselec-td .audio irequeneyiderived if-atom. theatre fbthersancrimbemehjeets bi mwintentiomre- -:q n y=se1ectingiwnm u izmyzinvmtmn. .aisidezimthe commutation ofimquezxcyr. selector-an By the method ctmaniameniia asseswew e uipmxumhwvin muns:wnraeeparaiinguindividuai nmotlnn u-i produ ed min all :physical ama s 41nd :audidrfimquenctesltronsnomplexaudio-inequalities-' a an ysis of: a complex waive @isaefiectecnwrtnimthe :-asisetkfortnunorei tuliyzlnmheispeclficatiomheresnnic on super-s nic raneewlnt irequency of-wibiza '1 :inatter 'intlcwin-gaby mtemnmtmthei cccomnanytivn w i h i e pparatus: ofsmysinmntian, -.cmgumwm g mm; mibratetransversely. Wane:-wavesmfls inln fm- Figurei luisaat hnmmntanseatinnahviow-wnrthe -1queney:havelorielnatedassounchwweeoesimflar "-mqumy .m'elentoraapnamtusi of myrzinwention mompressionalmawesflt .issneeessmm thmiomsto convert the same to transversely vibrating waves when involved in the analyzing system of my invention. Spectra of the sonic or super-sonic waves are formed, and the wave analysis is completed by introducing means throughout the spectrum for detecting the various component waves which may be present. Again, such components will be in the form of transversely vibrating waves, but may be transformed into sound or other form of energy Wave readily observable or employable, as desired.

My invention has numerous applications such as multiplex telegraph and telephone systems for separating carrier channels, television systems, synchroscope systems, systems of measurement using audio frequencies and in other audio frequency systems generally.

The main body is constructed of elastic material such as soft rubber. The body is shaped in the form of a sounding board or harp and includes a curved peripheral portion 2, a flattened portion 3, an acutely angled recessed portion 4 and a rounded end portion 5. Vibration transmitting member 6 is embedded in the body adjacent the rounded end portion and connected through arm 1 to an electromagnetic sound reproducing mechanism indicated at 8 giving out a complex modulated wave. Rods II, |2, l3, l4, l5, I6, I], IS, IS and 20 which extend through body I form a concave reflecting diifracting grating which reflects and difiracts modulated complex waves in a body of material, producing a spectrum at some surface indicated at 2|. The individual points or surface 2| will then be vibrating at separate frequencies. Small metal rods 3|, 32, 33, 34, 35, 35, 31, 38, 39, and 40 are embedded in the rubber body to take up or collect these vibrations. Onto these metal rods 3|, 32, 33, 3 4, 35, 36, 31, 38, 39 and 4|], coils 4|, 42, 43, 44, 45, 46, 41, 48, 49 and 50 are fastened'by means of arms Ma, 42a, 43a, 44a, 45a, 46a, 41a, 48a, 49a, 500., which are allowed to vibrate in a strong magnetic field established by permanent magnet 5| from which extends the magnetic core members 4|b, 42b, 43b, 44b, 45b, 46b, 41b, 48b, 49b, 50b, passing through the associated windings 4|, 4 43, 44, 45, 46, 41, 48, 49

. and 50-respectively as shown, thereby producing a potential of the same frequency as the rods 3|, 32, 33, 34, 35, 3'6, 31, 38, 39 and- 40. This voltage then is amplified by vacuum tube systems from which the useful separated individual currents of selected frequencies are taken. The multiple vacuum tube of my Letters Patent 2,210,010, dated Augustfi, 1940, can be used in place of a plurality of separate tubes.

The frame of the apparatus consists mainly of two metal plates 52 and 53 supported rigidly on their peripheries by side frame 54 and by rods 54a. The mass of the rubber or elastic material body is supported by a series of coil springs 55,

56, 51, 58, 59 and 30 disposed between the plates 52 and 53 and the body l as shown.

The difiracting grating composed of equally spaced rods H, |2, |3, |4, l5, l6, l1, l8, l9 and 2|] is supported rigidly in the frame 52-53 of the apparatus. The rods ll, |2, I3, 14, i5, i5, fi, |8, l9 and 2|! enter recesses in the plates 52-53 at each end as shown. Rods |2, l3, l4, l5, l6, l1, l8, l9, and 20 also adhere to the rubber -or elastic body L the rods 3|, 32, 33, 34, 35, 35, 31, 38, 39, and 40 4 will be vibrating at separate individual frequencies.

One of the basic features of the filter is that frequencies are separated by means of properties of waves due to their wave lengths in this material rather than by purely frequency characteristics. For this reason difliculties in the methods of separating out frequency by frequency characteristics are overcome.

In particular, the difficulties with respect to side bands do not enter into this method. The rods 3|, 32, 33, 34, 35, 36, 31, 38, 39 and 40 will vibrate at varying intensities according to the modulated waves that particular frequency may be subjected to but still will only be vibrating at one separate frequency.

The method of taking off the separate frequencies shown in Figs. 1-5 is only one of many that are possible. Systems in which resistance, capacities, potentials or currents may be varied by a moving member can'be used in place of the method shown in Figs. 1-5. For example the member that is embedded in the vibratory body I, as represented at 3| through 40, which serve as the transmitting means for selected vibrations, may have the arms 4|a-50a. extend to various electrical control means. In Fig. 13 I have shown the arm Me, for example, terminating in member 6| that enters a pool of mercury or graphite composition represented at 62, as contained in cup 63 and which serves as a variable resistance device in the input circuit of electron tube amplification system 64. The input circuit to the electron tube amplification system in cludes suitable source 65 in the series path leading to the grid circuit of the amplifier 64 so that the input circuit path may be varied in conductivity by physical displacement of member 6| in the respective pool 62 for varying the input to the amplifier circuit, in accordance with the audio frequency vibrations imparted to member 6| from the embedded member 3| in the massive body, I.

In place of the resistance change, I may employ a capacitance change, as represented in Fig. 14, in which arm 4 la is physically connected with movable capacity area 66 of variable condenser 61 associated with the stationary capacity area 53. The input circuit through the first stage of amplification of the amplifier system, represented at B4, is completed through resistor 69 in shunt with variable condenser 81. Vibrations transferred by arm 4|a variably displace plate 56 changing the effective capacity across the input circuit to the amplification system for repr'oduction of selected frequencies b'ycapacitance variations.

In lieu of the resistance and capacity methods, I may employ-an inductive variation 'method, as represented in Fig. 15, wherein-inductance 10 from the input circuit to-amplifier'channel 64 is variably acted upon- 'bymagneticarmature member 1| connected to arm:4|a so that armature member II is vibratedin accordance with the vibrations impressed upon embedded member 3|. Currents are generated"in winding I0 proportional to the displacement of armature within winding 10. Variations '-.-in=.inductive' effect of winding Ti thmbycontrol' the epesatien ef the amplification channel 64. Other means for exciting the input circuit ofthe amplification channel in accordance with vibratorylmotion imparted from the associated memberembeddedin the massive body may be employed for controllin different channels at selected frequencies.

The manner of impressing "audio frequencies 5 ubbh the massive body may also be varied and themethcds exijlal'ne'd herein are to be'cons'idered 1n the illustrative sense rather thanin'the llihit in'g s'eiiSe.

For example in Fig. 11 I have shown the vifira't'lDfi transmitting member 6 embedded in body I' connectedthrough arm 'I to the diaphragm I2 of an elect-r magnetic sound r'ep'r'oduclrig mechanism which developsacomplex modulated w'a've. The diaphragm T2- may carry a winding on a suitable coil su'riport represented at is, which isoberative within either a permssent or ah electrmmag'netidfield. Variations in the circuit of' the winding 14 carried-by c'Oil support I3 effect displacement of arm- 1' which in tl'lrh iiiifiaft's' angular movement to Vibration transmitting member 6; which rock within physical body I about a theoretical f-ulcr'urn 15 1mparting vibrations to the massiv'ebody I. I have designated the form of the reproduced impulse illustrated in Fig. 11 by letter A. I show by letter 1% in Fig. 12' the movement of vibration transnii't't'ing member 6 about a theoretical fulcrum T8" in the reverse direction for impressir'ig complex vibrations upon the member 6 through arm I as heretofore explained. Other methods of 'iii'o'u'nting the vibration transmitting member 6 with respect to the massive body I may be provided and the force transmitting dia'grarns A and 1?; are illustrative of a variety of mounting arrangements. 7

Figs. 6 arid- '7 Show circuit arrangements for i'm' ore'ssin'g' the selected frequencies on different channels for use 1n various applications; Windi'ngs M 42' and 13, associated with the magnetic system and core-member indicated at M b, 421) and [3b, whichare subjected to vibrations from the massive body I- through the link transfer member's Ha, it and 43a areillustrated as individually connected in the inputcircuits of separate channels constituted by electron tube systems 11, nan-a 1a. The outiiutcircuits-of these electrontubesystems are represented at 11", 1 a and 19' extending to selected channels for animation-1n indehendent' circuits.

Iii-lieu of the seifiarate time s stems shown at m and 19; I'may eihpidy amenable tube "'e or the disclosed in my Letters-Patent 2, 16-, 1'0, supra; wherein the vibratory windings 4- '1, ti and i=3- asson'a-ted with magnetic systems represented at 4 It; was and 4-111) connect to", indiwduai connoigrm elements of 'the"1'fiultible vacuum tube which inaveindicated generan-yp reference character in serving to segregate the desired frequehcles" into separate circuits leading to channels fr, it and 1'91 as aeeompnshed-m tneseparat e tnbesystem of Fig. 6.

Fig. lo'illustfates the manner in which transverse waves are established in the physical body I from the compiler frequencies impressed by v bratory de ice is on physical body]; The Wave strsss"firoddcedifi the physical body 1 result from the" displacement of vibratory member 6 alternately about itsubper and lower extremities a cor ing to positions A aind' Bin Figs. 11 and i2; resnefitireiy; where the mem er are illustraces micrdamig about Iflv'ots is and is. A and E ar produced in theyphysical mess I as represented at AJ-B in; Fig. was the vibratory-member epivets abbut fulcrum i and mica-um we in positions A and-Bin Figs. 11 and 2; rm-e nvely. compiex' waves as devei'op'ed memoer 6' n ver through the physical meager-bodyi auqspnkeuregratm "constituted in the-rods H; In; a; is, new; "Ii my hand 20' shown in Fig. 8. The number of rods in integrating bears no relation to the number of frequencies selectedfrom the spectrum, but isa factor in determining the extent and effectiveness 0'1 the spectrum itself. Likewise, the waves from the source 6 are not individually separated by the coaction of an individual rod of the grating; but by the cooperative action of all the rbdsasagrating, per se, a spectrum is produced in which the waves appear in the order of their frequencies. That 1's,the absence of any rod do'es net mean the absence of any frequency from the spectrum-this'seerhsto be abasic advantage of the device of my invention.

In Figs. 8 and 9 I have shown the theoretical prihcihles-inv-olved in the system or my invention. The rn-assive'bo'dy I may be of soft rubber as he'remore: explained or other materials may be used which are s'ufficie-ntly elastic to transmit transverse waves; The shape of the body, as has been previously explained, simulates the form of a sounding board or harp including the curved peripheral portion 2, the relatively flattened portion 3, the acutely angled recessed portion 4 and the rounded end portion 5. The rounded end portion 5' is substantially isolated from the portion 2| of the massive body so that complex frequencies generated at E in the massive body are directed to the grating. I-I'20 for reflection to the portion 2| of the massive body and direct transmission of transverse waves from the source 6 to the portion 21' is prevented. As will beobse-rved, the rod members II--2-U forming the grating are arranged ona curve represented at iii-drawn on aradius 82-. The transverse waves are established through the massive body I by reflection from the grating formed byrods I l--20 and directed to the portion 2i of the massive body. Portion 24- of the-massive body is formed on the periphery of a circle and a radius represented at 83. The distance within which the spectrum is confined in the massive body I is represented at 84 and within this distance the metal rods 3I4-fl are embedded along the portion 21 of the massive body as heretofore exnlained; In Fig. 8 it may be assumed that the complex frequencies at any instance which are impressed upon the massive body I of 6- include,

for example, frequencies l1, fa, and is. These frequencies establish transverse waves along the lines represented at- 85 which are reflected by certain of the rod members I-I--2-0-, representing the grating and individual frequencies directed to the portion-2i er massive body i which vibrates along the portion 21 at these individual frequencies. At the points whichare vibrating the individual selected irequencios th-esc vibrations are taken off by the rods I'll-40 and the transfer links 4Ia5llaassociated there-with for imparting vibratory movement to the particular vibratory means employed for generating currents correspending to the selected frequency. Each of-the generating means, such as 4 l '-49, are individually designed for generatin definite frequencies and discriminate and differ one from the ether-fer insuring selective generation of the individual frequencies for iii'i'fir'es'sioh anon thetrahs'nfitting chanfil's' in suitable manner such in jigs. 6 and '1 y In Fig. 9' I have represented the transverse waves established inthe massive body I wherein tlre"scfdrce includes frequencies f1, f2, 1'3, 1'4 aiidfs, etc. That is sdditronal'rrequencies f2 and}: are included in the complex frequencies impressed upon massive busy I rrenrscqrce e. fire additiciiail'liediie'iicies are rsn-set'ed'fren tlieg mtih g formed by rods |I--2ll and cause, through wave interference and the establishment of transverse waves, the weaving of the portion 2| of massive body I for setting up nodes along the portion 2| of the massive body I, at which are located the transfer means for selectively taking off the derived individual frequencies.

I have described my invention in certain of its preferred embodiments but I realize that modifications may be made in the arrangement and form of my invention and I intend no limitations upon my invention other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. Apparatus for separating frequencies com prising a massive body of substantially circular contour recessed adjacent one side thereof forming a projecting portion on said massive body, a generator of complex frequencies connected with the projecting portion of said massive body, for setting up compressional waves therein a grating embedded in said massive body in the path of the compressional waves established therein for transmitting compressional waves of selected frequency and establishing individual vibrations at the said frequencies at intervals adjacent the peripheral edge of said massive body substantially opposite said rating, and means connected at spaced intervals with the peripheral edge of said body for reproducing the frequencies isolated from said complex frequencies.

2. Apparatus for separating frequencies comprising a massive body of substantially circular contour recessed adjacent one side thereof forming a projecting portion on said massive body, a generator of complex frequencies connected with the projecting portion of said massive body, for setting up compressional waves in the massive body a grating comprising a plurality of spaced rods embedded in said massive body in the path of the compressional waves transmitted from said generator of complex frequencies, a multiplicity of frequency responsive members embedded in said massive body in substantially diametrically opposite positions with respect to the rods constitutin said grating, said frequency responsive members being substantially shielded from direct waves from said generator of complex frequencies, and means connected with the frequency responsive members for reproducing the'individual frequencies within the spectrum embraced by said generator of complex frequencies.

3. Apparatus for separating frequencies comprising a massive body of resilient material, means.

for resiliently suspendin said body for the passage therethrough of compresional waves in complex frequency, said body having a projection on one side thereof, a generator of complex frequen cies connected with said projection, a grating constituted by a multiplicity of rods embedded in said body along the periphery thereof substantially opposite to the projection thereon, a multiplicity of frequency responsive members embedded adjacent the peripheral edge of said body in positions substantially opposite to the positions occupied by the rods constituting said grating whereby the periphery of said body is vibrated at individual frequencies at spaced intervals by the last mentioned compressional waves, and means for individually reproducing individual frequencies through said frequency responsive members.

4. Apparatus for separating frequencies comprising a massive resilient body, yieldable means engaging opposite sides of said body for suspending said body for vibratory movement in space, means for impressing vibrations on said body adjacent one portion thereof, a grating embedded in said body in a position opposite the position in which the means for impressing vibrations upon said body is connected to said body, a multiplicity of frequency responsive members em bedded in said body adjacent the periphery thereof in position substantially opposite the position occupied by said grating, and means connected with said frequency responsive members for reproducing the frequencies individual to said members within the frequency range of said first mentioned means.

5. The method of separating frequencies which comprises impressing complex frequency vibrations upon a resilient suspended body for establishing compressional waves therethrough, alter nately reflecting and absorbing the compressional waves at spaced positions at one portion of the body for setting said body into vibration adjacent another portion thereof by reflected waves at different frequencies Within the range of the complex frequencies, and reproducing the diiferent frequencies at which the body is vibrating adjacent the last mentioned portion thereof.

6. The method of separating frequencies which comprises impressing complex frequencies upon a portion of a yieldable body, establishing compressional waves at the complex frequencies through the body, alternately reflecting and absorbing the compressional waves at spaced intervals adjacent one side of the body, transmitting the compressional waves at acute angles to the opposite side of the body, and establishing vibrations at the last mentioned side of the body at individual frequencies within the range of the impressed complex frequencies and separately reproducing the individual frequencies.

7. Apparatus for separating frequencies comprising a massive body of substantially circular contour recessed adjacent one side thereof forming a projecting portion on said massive body, means for supporting said body for substantially free vibration, a generator of complex frequencies connected with the projecting portion of said massive body for setting up compressional waves therein, a grating embedded in said massive body in the path of the compressional waves established therein for directing transverse waves of selected frequency and establishing individual vibrations at the said frequencies at intervals adjacent the peripheral edge of said massive body substantially opposite said grating, and electromagnetic means connected at spaced intervals with the last mentioned peripheral edge of said body for reproducing the frequencies isolated from said complex frequencies.

8. Apparatus for separating frequencies comprising a massive body of substantially circular contour recessed adjacent one side thereof forming a projecting portion on said massive body, means for supporting said body for substantially free vibration, a generator of complex frequencies connected with the projecting portion of said massive 'body for setting up compressional waves therein, a grating embedded in said arias-- sive body in the path of the compressional waves established therein for directing compressional waves of selected frequency and establishing individual vibrations at the said frequencies at intervals adjacent the peripheral edge of said massive body substantially opposite said grating, electromagnetic coil members supported by the peripheral edge of said massive body at the spaced intervals thereof vibrating at individual frequencies, magnetic core means spacially related to said electromagnetic coil members, and electronic means connected in circuit with said electromagnetic coil members for reproducing the frequencies isolated from said complex frequencies.

9. Apparatus for separating frequencies comprising a massive body of substantially circular contour recessed adjacent one side thereof forming a projecting portion on said massive body, means for supporting said body for substantially free vibration, a generator of complex frequencies connected with the projecting portion of said massive body for setting up compressional waves therein, a grating embedded in said massive body in the path of the compressional waves established therein for directing transverse waves of selected frequencies and establishing individual vibrations at the said frequencies at intervals adjacent the peripheral edge of said massive body substantially opposite said grating, variable capacity areas supported by the peripheral edge of said massive body at the spaced intervals thereof vibrating at individual frequencies, coacting fixed capacity areas adjacent said variable capacity areas, and electronic means connected across co acting pairs of said capacity areas for reproducing the frequencies isolated from said complex frequencies.

10. Apparatus for separating frequencies comprising a massive body of substantially circular contour recessed adjacent one side thereof forming a projecting portion on said massive body, means for supporting said body for substantially free vibration, a generator of complex frequencies connected with the projecting portion of said massive body for setting up compressional waves therein, a grating embedded in said massive body in the path of the compressional waves established therein for directing compressional waves of selected frequencies and establishing individual vibrations at the said frequencies at intervals adjacent the peripheral edge of said massive body substantially opposite said grating, magnetic core members supported by the peripheral edge of said netic core members.

11. Apparatus for separating frequencies comprising a massive body of substantially circular contour recessed adjacent one side thereof formgenerator of complex frequencies connected with the projecting portion of said massive body for setting up compressional waves therein, a grating comprising a multiplicity of spaced rods embedded in said massive body in the path of the compressional waves transmitted from said generator of complex frequencies, a multiplicity of frequency responsive members embedded in said massive body in substantially diametrically opposite positions with respect to the rods constituting said grating, said frequency responsive members being substantially isolated from direct waves from said generator of complex frequenportion of said body, and means electrically associated with the frequency responsive members for reproducing individual frequencies within the spectrum embraced by said generator of complex frequencies.

WALTER SOLLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,232,499 Clausen July 10, 1917 1,689,121 Ferdon Oct. 23, 1928 2,095,707 Kucher Oct. 12, 1937 2,169,304 Tournier Aug. 15, 1939 

